The invention relates to a portal milling machine, i.e. a milling machine in a portal type of construction, according to the preamble of the independent patent claims.
Portal milling machines of the type mentioned at the beginning are generally known. They have a machine bed and a portal firmly connected to the machine bed. On the portal, which normally comprises two vertical columns firmly connected to the machine bed and a crossbeam connecting these columns to one another, a milling unit provided with a milling spindle or a tool spindle is arranged so as to be movable in a translatory manner in a first direction (Z) and a second direction (Y) transversely to the machine longitudinal axis (X) defined by the portal passage. Furthermore, portal milling machines of said type have a plane linear guide firmly connected to the machine bed. The linear guide is arranged essentially horizontally in the machine longitudinal direction (X), i.e. in the X-direction. It leads through the portal and serves to guide a slide which is movable in the X-direction through the portal and carries a work mounting device, typically in the form of a work table. Such portal milling machines are normally designed and arranged in such a way that the translatory direction of movement X runs essentially horizontally through the portal, the translatory direction of movement Z runs essentially vertically, and the translatory direction of movement Y runs essentially horizontally and at right angles to the X-direction.
Compared with single-column milling machines in a C-type of construction, which have a single, essentially vertical column, to which an extension arm carrying the milling unit is attached at the top and which is firmly connected to the machine bed at the bottom, the machine bed carrying a work table, portal milling machines have advantages with regard to the rigidity of the machine. The structure closed upon itself, consisting of the portal and the machine bed, can absorb greater forces, given the same dimensioning, than the structure, open on one side, of a single-column machine in a C-type of construction.
On the other hand, portal milling machines are less suitable for automated operation than single-column machines in a C-type of construction. On the one hand, in portal milling machines, the chip disposal is problematic, since the chips produced during the milling tend to remain sitting on the linear guide leading through the portal or on the chip cover guard of the linear guide. On the other hand, the accessibility to the tool processing point lying in the region of the portal and thus to the tool and to the workpiece is restricted by the portal.
The object of the invention is to specify a milling machine in a portal type of construction which can be readily automated and in particular ensures good accessibility to the tool processing point and permits good chip disposal.
The solution of the object is defined by the features of the independent patent claims. According to the invention, a portal milling machine has an elongated machine bed, the longitudinal direction of which defines an X-direction (also designated as machine longitudinal direction). Furthermore, the portal milling machine is provided with a portal which is arranged at right angles to the X-direction and has an elongated plan form, the longitudinal direction of which defines a Y-direction (also designated as portal longitudinal direction) (running at right angles to the X-direction). A milling unit is arranged on the portal so as to be movable in a translatory manner in a first direction and a second direction transversely to the X-direction, and a linear guide which leads through the portal in the X-direction and is intended for a slide carrying a work mounting device and movable in the X-direction is attached to the machine bed. In plan form, a part of the machine bed projects beyond the portal in the X-direction at least on one side, in which case this projecting part of the machine bed may also be the entire machine bed. According to the invention, the machine bed, with regard to the portal, is offset in the Y-direction toward one longitudinal end of the portal in such a way that, in the region of the angle enclosed between the projecting machine bed part and the portal, good accessibility to the working region of the machine in the region of the portal center is ensured from the other longitudinal end of the portal.
Due to the asymmetrical type of construction with regard to a vertical center plane running in the X-direction through the portal center, good accessibility to the tool processing point in the optimum working region of the machine, namely in the region of the portal center, is provided on the one hand. An operator can come from the side comparatively close up to the slide carrying the work mounting device or to the work processing point. This proves to be advantageous, e.g. when setting the machine for new machining operations, and helps to improve the ergonomics of the portal milling machine according to the invention. On the other hand, space is also created on the portal side remote from the machine bed, and this space may be utilized for the installation of the chip conveying device. On the whole, this provides for the possibility of automated operation of the portal milling machine.
The machine bed, with regard to the portal center, may be offset in the Y-direction toward the one longitudinal end of the portal by more than one sixth, preferably even by more than two sixths, of the clear width of the portal passage, in order to create sufficient space in the region of the other longitudinal end of the portal.
In the portal milling machine according to the invention having an asymmetrical type of construction, the portal is preferably arranged relative to the machine bed such that the structure formed from the portal and the machine bed has essentially a plan form like a two-legged right angle, one leg being formed by the machine bed plan extending in the X-direction and the other leg being formed by the portal plan extending in the Y-direction. In this case, the machine bed is arranged so as to be offset completely toward one longitudinal end of the portal and it projects in the X-direction beyond the portal merely on one portal side. As a result, an especially simple and compact structure of the machine is achieved overall.
According to a preferred embodiment of the invention, the linear guide is a plane linear guide arranged essentially horizontally (i.e. running in the horizontal direction), the guide plane of the linear guide, relative to the horizontal, being inclined by an angle transversely to the X-direction in such a way that chips produced during the milling fall down solely on account of the force of gravity from the linear guide or from a cover protecting the latter from the chips.
Throughout the present description and the claims, the expression xe2x80x9clinear guidexe2x80x9d (also designated as straight guide) refers to a bearing for guiding parts moving rectilinearly. A linear guide is designated as plane if it defines a guide plane extending in the guide longitudinal direction. In the case of a linear guide having an essentially flat, plane guide bed, the guide plane is determined by the guide bed surface. In this case, the guide bed surface need not be completely plane, but rather may be provided with passages, recesses, reinforcing ribs or similar structures which deviate in sections from the plane form of the guide bed surface. In a linear guide which comprises essentially a single, flat guideway (e.g. a flat guide or a dovetail guide), the guideway surface may be designated as guide plane of the linear guide. If a linear guide comprises two parallel rails or slideways, the plane determined by the two parallel rails or slideways may be designated as guide plane. If a linear guide is designed as a profiled rail guide having an essentially plane profile surface, to which a plurality of parallel guide rails are attached, this profile surface may be designated as guide plane of the linear guide.
According to the abovementioned preferred embodiment of the invention, the guide plane of the plane linear guide running through the portal is considerably inclined like an inclined bed guide transversely to the guide direction. The considerable inclination of the guide plane achieves the effect that chips which are produced during the milling operation and fall onto the linear guide or onto a cover provided for protecting the linear guide from chips do not remain lying on the linear guide or the chip guard cover but slip off the latter on account of the force of gravity. As a result, good chip disposal is achieved, a factor which is a precondition for automating the portal milling machine.
Furthermore, the considerable inclination of the guide plane enables a work changing device, possibly arranged laterally next to the linear guide, to be arranged closer to the slide carrying the work mounting device, i.e. the X-slide, than would be possible in the case of a plane linear guide having a horizontal guide plane. As a result, the times for the workpiece change can be reduced, which helps to increase the productivity of the portal milling machine according to the invention.
In addition, on account of the considerable inclination or angular setting of the guide plane of the linear guide, the accessibility to the machine center in the region of the portal center is further improved. An operator can come from the side closer to the slide carrying the work mounting device or to the tool processing point than would be possible in the case of a plane linear guide having a horizontal guide plane.
Furthermore, the angular setting of the guide bed or of the guide plane of the linear guide enables the slide carrying the work mounting device to be mounted at various heights in a comparatively simple manner. As a result, the portal milling machine according to the invention can be better adapted for machining workpieces having different dimensions. In addition, the angular setting of the guide plane of the linear guide makes is possible for the slide having the work mounting device to be installed in such a way that, despite the machine bed being offset from the portal center to one portal end, it can be moved centrally through the portal (and thus through a region favorable for the workpiece machining) by the slide being arranged essentially laterally on the linear guide.
The guide plane of the linear guide, relative to the horizontal, is preferably inclined transversely to the X-direction by an angle which is greater than 40 degrees, preferably even greater than 60 degrees. In particular, this angle may also be approximately 90 degrees. For heavy X-slides, a rather small angle of inclination of, for example, approximately 45 degrees is preferred. A comparatively small angle of inclination of the guide plane ensures better seating of the heavy slide on the linear guide. On the other hand, angles of inclination which are rather larger are preferred for light X-slides in order to ensure that the chips slip off the linear guide or its chip guard cover in an optimum manner. In particular, an angle of inclination of 90 degrees may also be used for light slides. In this case, the guide plane or the guide bed of the linear guide is arranged vertically.
However, variants of the invention in which the guide plane of the linear guide, relative to the horizontal, is inclined transversely to the X-direction by an angle which is greater than 90 degrees are also possible. The guide plane and the guide bed are then arranged in an overhanging manner, so that the X-slide is guided in a suspended manner on the linear guide. In this variant of the invention, the linear guide is protected in an especially effective manner from chips falling down.
In a portal milling machine according to the invention, the linear guide is preferably designed in such a way that the X-slide can alternatively be mounted at various heights on the linear guide. This permits simple adaptation of the portal milling machine for machining workpieces having different sizes. For this purpose, depending on the application, tables having different machining heights may be mounted. The possibility of being able to mount the X-slides at various heights when using rotary and/or swivel tables for 5-axis machining proves to be especially advantageous. Such tables are relatively tall and accordingly restrict the passage or the workpiece size in conventional portal machines.
The portal machine according to the invention may have a further slide (Y-slide) which is arranged on the portal so as to be movable in the horizontal Y-direction transversely to the X-direction, the milling unit in the form of a spindle head provided with a milling spindle being arranged on this Y-slide so as to be movable in the vertical Z-direction. This embodiment of the invention is especially suitable for high-speed milling, since only comparatively small masses have to be moved in order to move the spindle head. As an alternative to this, however, a portal milling machine according to the invention may also comprise a portal having a cross member which is movable in the vertical Z-direction and on which a spindle head movable in the Y-direction is arranged.
According to a further advantageous variant of the invention, in a portal milling machine comprising a portal on which a milling unit is arranged so as to be movable in a translatory manner in a first direction (Z) and a second direction (Y) transversely to the machine longitudinal direction (X), and comprising an elongated machine bed to which a plane linear guide which leads essentially horizontally through the portal in the machine longitudinal direction (X) and is intended for a slide carrying a work mounting device and movable in the X-direction, the structure formed from the machine bed and the portal is designed as a monolithic, homokinetic block (also designated as monoblock). The design of the structure comprising the machine bed and the portal as a monoblock ensures good thermal conduction between the various parts of the structure and good rigidity of the structure. Such a portal milling machine with a monoblock structure may of course also be provided with a considerably inclined guide plane of the plane linear guide extending in the X-direction and/or with a machine bed arranged so as to be offset with regard to the portal center toward one longitudinal end of the portal. However, the aspect of designing the structure comprising the machine bed and the portal as a monoblock also proves to be advantageous irrespective of the considerable inclination of the guide plane of the plane linear guide extending in the X-direction or of the machine bed arrangement offset with regard to the portal center.
In a portal milling machine with a monoblock structure, the entire monoblock is preferably produced from polymer concrete. In principle, however, other materials suitable for the construction of portal milling machines, e.g. steel, may also be used.
The monoblock structure may be composed of individual castings. In this case, the individual castings may be produced from a uniform casting material, intermediate spaces possibly present between the castings after the assembly of the individual castings to form the desired structure being filled with the same casting material in order to produce a homogeneous connection between the castings with regard to the material. In this way, complicated monoblock structures can also be produced.
The portal is preferably designed as a one-piece casting into which the machine bed, likewise designed as a one-piece casting, is inserted, the machine bed being designed as a support to which the linear guide is attached. In this way, portal milling machines having X-guides or X-strokes of different length can be produced in a relatively simple and cost-effective manner.
In the case of a comparatively simple form, however, the entire structure formed from the machine bed and the portal may also be designed as a one-piece casting. This makes possible exceptionally simple manufacture of this structure. In addition, especially good rigidity and thermal conductivity of the structure are achieved.
Further advantageous embodiments and feature combinations of the invention follow from the detailed description below and all the patent claims in their entirety.